Stereopure Functionalized Benzosultams via Ruthenium(II)-Catalyzed Dynamic Kinetic Resolution-Asymmetric Transfer Hydrogenation

A highly diastereo- and enantioselective Ru(II)-catalyzed dynamic kinetic resolution-asymmetric transfer hydrogenation (DKR-ATH) of alpha-(N-sulfonylimino) and alpha-(N-sulfonylamino) aryl ketones to 4-hydroxy-benzo-delta- and 3-(alpha-hydroxy-arylmethyl)-benzo-gamma-sultams is presented. By employing enantiopure ansa-Ru[PipSO(2)DPEN(CH2)(4)Ph] cat. II with S/C = 10 000 in a HCO2H/Et3N binary mix, up to > 99.9% ee and dr > 99:1 are obtained with 100% conversion under mild conditions. Application to access the stereopure structurally simplified TsDPEN N,N-ligand syn-3-(alpha-aminobenzyl)-benzo-gamma-sultam (syn-ULTAM) and its structural isomer trans-4-amino-3-phenyl-benzo-delta-sultam (trans-4) is demonstrated.